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1.
Eddie Wadbro Sara Zahedi Gunilla Kreiss Martin Berggren 《BIT Numerical Mathematics》2013,53(3):791-820
A finite element method for elliptic partial differential equations that allows for discontinuities along an interface not aligned with the mesh is presented. The solution on each side of the interface is separately expanded in standard continuous, piecewise-linear functions, and jump conditions at the interface are weakly enforced using a variant of Nitsche’s method. In our method, the solutions on each side of the interface are extended to the entire domain which results in a fixed number of unknowns independent of the location of the interface. A stabilization procedure is included to ensure well-defined extensions. We prove that the method provides optimal convergence order in the energy and the L 2 norms and a condition number of the system matrix that is independent of the position of the interface relative to the mesh. Numerical experiments confirm the theoretical results and demonstrate optimal convergence order also for the pointwise errors. 相似文献
2.
The effective utilization of the cryogenic exergy associated with liquefied natural gas (LNG) vaporization is important. In this paper, a novel combined power cycle is proposed which utilizes LNG in different ways to enhance the power generation of a power plant. In addition to the direct expansion in the appropriate expander, LNG is used as a low-temperature heat sink for a middle-pressure gas cycle which uses nitrogen as working fluid. Also, LNG is used to cool the inlet air of an open Brayton gas turbine cycle. These measures are accomplished to improve the exergy recovery of LNG. In order to analyze the performance of the system, the influence of several key parameters such as pressure ratio of LNG turbine, ratio of the mass flow rate of LNG to the mass flow rate of air, pressure ratio of different compressors, LNG pressure and inlet pressure of nitrogen compressor, on the thermal efficiency and exergy efficiency of the offered cycle is investigated. Finally, the proposed combined cycle is optimized on the basis of first and second laws of thermodynamics. 相似文献
3.
Ahmad Seif Ehsan Zahedi Goodarz M. Rozbahani 《Central European Journal of Chemistry》2012,10(1):96-104
To investigate the influence of C-doping on the electrostatic structure properties in the frame work of density functional
theory (DFT), we considered beryllium monoxide nanotubes (BeONTs), consisting of 60 Be and 60 O atoms. Full geometry optimizations
are performed for all structures, i.e., all atoms are allowed to relax. Afterwards, the chemical shielding (CS) tensors are
calculated for Be-9, O-17 and C-13 nuclei in the C-doped forms and also pristine models of the (10, 0) zigzag and (5, 5) armchair
BeONTs. Formation energies indicate that C-doping of Be atom (CBe form) could be more favorable than C-doping of O atom (CO
form) in both zigzag and armchair BeONTs. Gap energies and dipole moments detected the effects of dopant in the (5, 5) armchair
models; however, those parameters did not indicate any significant changes in the C-doped (10, 0) zigzag BeONT models. The
results show that the CS values for the Be and O atoms-contributed to the Be-C bonds or those atoms close to the C-doped region-in
the CO form of BeONTs (zigzag and armchair) are changed. The same values only for the O atoms-contributed to the O-C bonds-
in the CBe form of BeONTs (zigzag and armchair) are changed. 相似文献
4.
Optimization of synthesis procedure and structure characterization of manganese tungstate nanoplates
Mehdi Rahimi-Nasrabadi S. Mahdi Pourmortazavi Morteza Khalilian-Shalamzari S. Somayyeh Hajimirsadeghi M. Mahdi Zahedi 《Central European Journal of Chemistry》2013,11(8):1393-1401
A simple and fast chemical method was used for synthesis of manganese tungstate nanoplates in flower-like clusters; while Taguchi robust design was employed as statistical method for optimization of the experimental parameters for the procedure. Ultrafine manganese tungstate plates in flower-like clusters were synthesized via a direct precipitation method involving addition of manganese ion solution to the aqueous tungstate reagent. Effects of various reaction conditions such as manganese and tungstate concentrations, flow rate of reagent addition and reactor temperature on the thickness of the synthesized manganese tungstate plates were investigated experimentally. Analysis of variance (ANOVA) showed that manganese tungstate nanoplates could be effectively synthesized by tuning significant parameters of precipitation procedure. Meanwhile, optimum conditions for synthesis of MnWO4 nanoplates via this simple, fast, and cost effective method were proposed. The structure and composition of the prepared nanoplates under optimum conditions were characterized by EDX, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), FT-IR spectroscopy, and photoluminescence techniques. 相似文献
5.
Fereshteh Rezaei Nahid Pirhady Tavandashti Ali Reza Zahedi 《Research on Chemical Intermediates》2014,40(3):1233-1247
Polyaniline nanofibers are readily synthesized by bulk polymerization; ammonium per sulphate (APS) is used as oxidizing agent and hydrochloric acid as dopant without any hard or soft templates. A detailed study was conducted on the effect of a variety of synthetic conditions on the size and morphology of the polyaniline nanostructure. These conditions include the concentration of dopant, and the APS-to-aniline and acid-to-aniline molar ratios. The morphology of the nanofibers was confirmed by SEM and TEM. XRD and FT-IR and UV–visible spectroscopy were used for structural characterization of nanofibers. The results showed that not only the microstructure of the polyaniline product, but also other characteristics, for example conductivity, crystallinity, and, more importantly, the efficiency of the process are strongly affected by the synthetic conditions. 相似文献
6.
Roya Zahedi Faramarz Afshar Taromi Seyed Heidar Mirjahanmardi Mehdi Nekoomanesh Haghighi Roghayeh Jamjah Khosrow Jadidi 《Polymer Science Series B》2016,58(2):143-151
Two new ethers were synthesized using the Williamson reaction from related alcohols and were used as external donors in propylene polymerization in the presence of the industrial diisobutyl phthalate-based MgCl2-supported Ziegler-Natta catalyst. For comparison the propylene polymerization was carried out in the presence of silane and in the absence of external donors. The produced polymers were characterized by differential scanning calorimetry, xylene extraction, melt flow index, scanning electron microscopy and gel permeation chromatography. The isotacticity, molecular weight and molecular weight distribution, melt flow index, crystallinity degree and thermal properties of polypropylenes were influenced by the type of external donors. 相似文献
7.
Payam Zahedi Iraj Rezaeian Seyed‐Omid Ranaei‐Siadat Seyed‐Hassan Jafari Pitt Supaphol 《先进技术聚合物》2010,21(2):77-95
Wound dressings have experienced continuous and significant changes since the ancient times. The development starts with the use of natural materials to simply cover the wounds to the materials of the present time that could be specially made to exhibit various extraordinary functions. The modern bandage materials made of electrospun biopolymers contain various active compounds that are beneficial to the healing of wounds. These materials are fibrous in nature, with the size of fibers segments ranging from tens of nanometers to micrometers. With the right choices of biopolymers used for these fibrous materials, they could enhance the healing of wounds significantly compared with the conventional fibrous dressing materials, such as gauze. These bandages could be made such that they contain bioactive ingredients, such as antimicrobial, antibacterial, and anti‐inflammatory agents, which could be released to the wounds enhancing their healing. In an active wound dressing (AWD), the main purpose is to control the biochemical states of a wound in order to aid its healing process. This review provides an overview of different types of wounds, effective parameters in wound healing and different types of wound dressing materials with a special emphasis paid to those prepared by electrospinning. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
8.
The electron transport properties of furan, thiophene and selenophene dithiols based molecular wires through two electrodic systems using non-equilibrium Green’s functions technique (NEGF) are investigated. The electron transport of the above systems is systematically studied by analysis of transmission function, density of states, current–voltage characteristics, and conductance of the systems. The maximum current is occurred at the vicinity of 2.0 V and the values are 90.37, 98.82 and 100.31 μA for furan, thiophene and selenophene dithiols, respectively. These results can be attributed to the molecular projected self consistent Hamiltonian (MPSH) of two electrodic systems with different molecules at different bias voltage and also to quality of resonance of π electrons of heterocyclic ring. We can foresee that the furan, thiophene, and selenophene dithiols can be applied at electronic devices because of switching the high and low current. 相似文献
9.
Ehsan Zahedi 《Physica B: Condensed Matter》2011,406(8):1592-1597
Ammonia adsorption on the external surface of C30B15N15 heterofullerene was studied using density functional calculations. Three models of the ammonia-attached C30B15N15 together with the perfect model were optimized at the B3LYP/6-31G? level. The optimization process reveals that dramatic influences occurred for the geometrical structure of C30B15N15 after ammonia adsorption; the B atom relaxes outwardly and consequently the heterofullerene distorts from the spherical form in the adsorption sites. The chemical shielding (CS) tensors and nuclear quadrupole coupling constants of B and N nuclei were calculated at the B3LYP/6-311G** level. Our calculations reveal that the B atom is chemically bonded to NH3 molecule. The B atom in the NH3-attached form has the largest chemical shielding isotropic (CSI) value among the other boron nuclei. The CQ parameters of B nuclei at the interaction sites are significantly decreased after ammonia adsorption. 相似文献
10.
This study presents an easy and cost-effective flow-based cloud point extraction (CPE) method for determining partial amounts of two organophosphorus pesticides (phosalone and ethion) in seawater by HPLC–UV–Vis. In continues CPE methodology, the effect of the different column packing type such as carbon nanotube, polyacrylonitrile nanofiber and fiberglass on pesticide extraction was investigated. The Triton X-100 was utilized as nonionic surfactant, and moreover, effect of different parameters such as pH, temperature, extraction time, surfactant concentration, type and volume of the eluent solution on the extraction efficiency was optimized. Under optimum conditions, the figures of merit of the method for phosalone and ethion were obtained as: the enrichment factor (172 and 166), line range (0.8–300 and 0.5–300 µg L?1, R 2 = 0.9973 and 0.9982), relative standard deviation in concentration of 200 µg L?1 (%RSD = %5.4 and %7.99, N = 5) and limit of detection (LOD = 0.24 and 0.14 µg L?1). The suggested method was successfully used for determination of phosalone and ethion in Chabahar Bay seawaters with satisfactory results. 相似文献